Resistance to known antimalarial therapies is becoming an increasing problem and new therapies are therefore desperately needed. Upon infecting a host, the malaria parasite avidly consumes the host hemoglobin as its source of nutrients. Plasmepsin I and II are proteases from Plasmodium falciparum that are necessary during the initial stages of hemoglobin hydrolysis and digestion, which primarily occurs in the .alpha.chain, between Phe 33 and Leu 34, although other sites may serve as substrates for hydrolysis as well. It has been shown in cultures inhibition of plasmepsin by a peptidomimetic inhibitor is effective in preventing malarial hemoglobin degradation and in killing the parasite (Francis, S. E., Gluzman, I. Y. Oksman, A., Knickerbocker, A., Mueller, Bryant, M. L., Sherman, D. R., Russell, D. G., and Goldberg, D. E. (1994) EMBO J, 13, 306-317). Thus, persons of skill in the art expect that plasmepsin inhibitors will provide effective antimalarial therapy.
Cathepsin D is a human protease in the endosomal-lysosomal pathway, involved in lysosomal biogenesis and protein targeting, and may also be involved in antigen processing and presentation of peptide fragments. The protease therefore displays broad substrate specificity but prefers hydrophobic residues on either side of the scissile bond.
Cathepsin D has been implicated in a variety of diseases, including connective tissue disease, muscular dystrophy, and breast cancer. Most recently, cathepsin D is believed to be .gamma.-secretase, the protease which processes the .beta.-amyloid precursor protein to generate the C-terminus of .beta.-amyloid (Dreyer, R. N., Bausch, K. M., Fracasso, P., Hammond, L. J., Wunderlich, D., Wirak, D. O., Davis, G., Brini, C. M., Bucholz, T. M., Konig, G., Kamark, M. E., and Tamburini, P. P. (1994) Eur. J. Biochem., 224, 265-271 and Ladror, U.S., Synder, S. W., Wang, G. T., Holzman, and Krafft, G. A. (1994) J. Biol. Chem., 269, 18422-18428), which is the major component of plaque in the brains of Alzheimer's patients. Consequently, persons of skill in the art expect that inhibitors of cathepsin D will be useful in treating Alzheimer's disease.
The present invention relates to amino acid (statine) analogs and their inhibitory action against aspartyl proteases, and more particularly, the invention relates to the identification of amino acid analogs that display selective inhibitory activity against plasmepsin and cathepsin D. Although statine-containing peptides are known which inhibit aspartyl proteases (Shewale, J. G.; Takahashi, R.; Tang, J., Aspartic Proteinases and Their Inhibitors, Kostka, V., Ed. Wlater de Gruyter: Berlin (1986) pp 101-116), there are only a few selective inhibitors for cathepsin D (Lin, T. Y.; Williams, H. R., Inhibition of Cathepsin D by Synthetic Oligopeptides, J. Biol. Chem. (1979), 254, 11875-11883; Rich, D. H.; Agarwal, N. S., Inhibition of Cathepsin D by Substrate Analogues Containing Statine and by Analogues of Pepstatin, J. Med. Chem. (1986) 29 (2519-2524), and for plasmepsin (Silva, A. M. et al., Structure and Inhibition of Plasmepsin II, A Hemoglobin-Degrading Enzyme From Plasmodium falciparum, Proceed Natl Acad Sci, 1996, 93, 10034-10039). The present invention also relates to the solid phase synthesis of such amino acid analogs.